Computers and similar equipment have had the capability for a number of years to communicate via telephone lines through the use of modems and telephones. The general practice has been for the user to power-up his own computer and then, by means of a telephone, "call up" a computer operating at a remote location. If a user desired to receive messages on his computer, he was obliged to leave the computer powered up during the time in which he wished to receive data transmissions. Without leaving the computer on, the user gave up the ability to send and receive those transmissions.
The practice of leaving one's telecomputing equipment powered up while unattended has many disadvantages. The computer which is powered up and left unattended represents an increased safety hazard which can risk damage to either the computer itself or its surrounding environment, or both. There is continuous power consumption as well as equipment damage susceptibility due to power failures. Further, numerous extended periods of operation will decrease the reliability of the computer and its useful life will be significantly shortened.